This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Membrane trafficking pathways are essential for normal physiological processes such as signal transduction, antigen presentation, organelle biogenesis, and many others, and for pathophysiological processes such as HIV budding. Membrane trafficking via endosomes is carried out by a series of multi-protein complexes, including the ESCRT complexes and the retromer complex. We have obtained a series of crystal structures of the cores of these assemblies, and in combination with the structures of individual domains and homology modeling, models for the complete structures can be generated. The models have been assessed by comparison to hydrodynamic studies of multiple truncation constructs, providing constraints on the solution structures of the intact complexes. We have applied coarse-grained Monte Carlo simulations using residue-based potentials with rigid domains and core structures to model the assemblies.